The present invention generally relates to electron beam exposure systems, and more particularly to an electron beam exposure system that has a large number of electric connections extending into an evacuated column, in which the electron beam travels, for supplying various signals to the elements provided inside the column.
The electron beam exposure system writes a pattern on an object by a focused electron beam. By using the focused electron beam, one can write a pattern on the object which may be a semiconductor wafer, with a resolution well below 1 .mu.m.
In order to achieve the object, the electron team exposure system employs electron lenses that produce a very strong magnetic field. Generally, an electron lens having the strength of several hundred to several thousand ampere-turns is employed for focusing the electron beam. Such an electron lens is bulky and occupies a considerable space around the column of the electron beam exposure system.
FIG. 1 shows schematically the general construction of a conventional electron beam exposure system that employs the blanking aperture array system.
Referring to FIG. 1, an electron beam is emitted from an electron gun 30 and travels along a predetermined optical path 64 toward a semiconductor wafer 56. The electron beam 32 is thereby shaped by an aperture 34 and focused by a first electron lens 36. The electron beam 32 is then deflected by an electrostatic deflector 38 for beam alignment and passed through another electron lens 40. In the electron lens 40, the electron beam is shaped into a parallel beam and passed through a blanking aperture array 42.
The blanking aperture array 42 comprises a plate carrying thereon a number of apertures arranged in a row and column formation. Each aperture forms an electrostatic deflector and passes or interrupts the parallel electron beam incident thereto in response to a control signal applied to the electrostatic deflector of the aperture. Thus by passing the electron beam through the blanking aperture array 42, the electron beam is shaped or "patterned" as desired.
The patterned electron beam is then focused by an electron lens 44 and focused on the wafer 56 after passing through the electron lenses 48, 52 and 59. Further, electrostatic deflectors 46 and 62 are provided between the lens 44 and the wafer 56, wherein the electrostatic deflector 46 is used for turning off the electron beam, while the electrostatic deflector 62 is used for deflecting the electron beam on the wafer 56. Further, there are provided adjustment coils 58 and 60 respectively in correspondence to the electron lenses 52 and 59.
In such an electron beam exposure system, it should be noted that a large and bulky coils have to be provided around an evacuated column 100 in which the electron beam passes through. Referring to FIG. 1, coils 36a, 40a, 44a, 48a, 52a and 59a are provided to surround the column 100. It should be noted that the strength of these electron lenses has to be large in order to obtain a satisfactory resolution. When the strength of the electron lens is reduced, the focal length is increased and various problems, like spherical aberrations, chromatic aberrations as well as the problems caused by the coulomb interaction of electrons, may occur.
In order to obtain a strong electron lens, one has to supply a large current to the coils forming the lens, and thereby the size of the electron lens increases inevitably. When the size of the coil is reduced, the heating caused by the large current flowing through thin wires of the coil becomes excessive and the magnetic field formed by the coil becomes unstable. Under such situation, it will be understood that the column 100 is almost entirely surrounded by the coils and little space is available for the interconnection interface to the elements inside the column such as the electrostatic deflectors or adjusting coils. As the column 100 has to be formed by a conductive material, the electrostatic deflectors cannot be provided outside the column 100.
This problem of difficulty in finding the location for the interconnection interface becomes particularly serious in the recently developed electron team exposure systems that employ the blanking aperture array. Such electron beam exposure systems need a large number of interconnection leads for supplying various control signals for patterning the electron beam.
FIG. 2 shows a conventional element 10 used for supplying control signals to the elements provided inside the column 100.
Referring to FIG. 2, the element 10 comprises a ring 12 of a metal and the like, and a number of insulating sleeves 16 are provided in the ring 12 to extend radially. Further, each sleeve 16 includes therein an interconnection lead 20.
FIG. 3 shows the partial cross section of the side view of the element 10. Referring to FIG. 3, the blanking aperture array 42 is provided inside the ring 12 where the array 18 is connected to the leads 20 in the sleeves 16 by respective interconnection wires 22. The ring 22 has upper and lower flanges 22a and 22b in intimate contact with corresponding flange parts 110a and 100b formed in the column 100 and establishes a hermetic seal with the flange surfaces. In this conventional element 10, it will be understood that there is a limitation in the number of leads 20 that can be provided in one element, as the leads cannot be placed closer than the diameter of the sleeve 16. Generally, such a conventional element 10 has a thickness of 20-30 mm and occupies considerable space.
In the conventional type electron exposure system that does not use the blanking aperture array 42, the element 10 is provided generally between the coil 52a for the demagnification lens 52 and the coil 59a for the objective lens 59, for supplying the control signals to the adjusting coil 58 in the lens 52, the adjusting coil 60 in the lens 59, and to the electrostatic deflector 62, as schematically shown in FIG. 1. The placement of the element 10 below the coil 59a is not desirable, as such a construction increases the distance between the objective lens 59 and the wafer 56. Even so, one has to compromise about the resolution in order to provide the element 10.
In the recent electron beam exposure systems that employ the blankinq aperture array it will be understood that another interface element 10 has to be provided in correspondence to where the blanking aperture array is provided. This can only be done by increasing the distance between the electron lens 40 and the electron lens 44 and insert the element 10 into the space thus formed. However, such an increase in the separation between the lenses requires undesirable increase in the focal length of the lenses.
FIGS. 4 and 5 show the blanking aperture array 42 in some detail. Referring to the perspective view of FIG. 4, the blanking aperture array 42 includes a number of apertures 88 arranged in the row and column formation, and each aperture 88 has a pair of electrodes 90 and 93, 91 and 92, . . . as shown in FIG. 5 for deflecting the electron beam passing through the aperture 88. When the electron beam is deflected upon passage through the aperture 88, the electron beam does not reach the wafer 56 while when there is no deflection, a dot pattern corresponding to the aperture 88 is written on the wafer 56. Thus, by suitably driving the electrodes for each aperture 88, one can pattern the electron beam that reaches the wafer 56 as desired.
In order to drive the electrodes of the apertures 88 individually, it is necessary to provide a large number of leads 94, 95, 96, 97, . . . on the body of the blanking aperture array 42 in correspondence to the rows and columns of the apertures 88. This means that a large number of control signals have to be supplied to the blanking aperture array 42 in addition to the control signals to the adjustment coils 58, 60 and the electrostatic deflector 62. Thus, it will be understood that the conventional element 10 is insufficient for supplying the control signals to the electron beam exposure system that uses the blanking aperture array. On the other hand, there is an acute demand for such an electron beam exposure system that uses the blanking aperture array particularly in relation to the fabrication of large capacity semiconductor memories that requires a submicron patterning with a high throughput.